Enzymes in the retina are capable of mediating the oxidation or reduction of certain alcohols and aldehydes. Two such compounds are Vitamin A alcohol (retinol) and Vitamin A aldehyde (retinaldehyde), both of which are of central importance in the metabolism of visual pigment. It has been generally thought that the interconversion of retinol and retinaldehyde is mediated by "hepatic-type" alcohol dehydrogenase (ADH, E.C. 1.1.1.1). The results of experiments by this investigator and others suggest that the oxidation-reduction of Vitamin A in the retina is catalyzed by an enzyme which differs physically and kinetically from the hepatic enzyme. Furthermore, the retinal oxidation-reduction of low molecular weight substrates (e.g. ethanol, acetaldehyde) appears to be mediated by an enzyme different than "retinol dehydrogenase" or "retinaldehyde reductase". In the present project experiments are designed to compare the retinal enzymes of the rat, cow, monkey and human which catalyze the metabolism of alcohols and aldehydes, including Vitamin A. These enzymes will be partially purified and characterized with respect to physical and kinetic parameters. Part of this project will consist of examining in vitro and in vivo the relationship of these retinal enzymes to the visual disturbances associated with certain "retinotoxic" chemicals and hereditary retinal diseases. This project, by studying directly the retinal enzymes of alcohol oxidation and aldehyde reduction, will not only provide additional information about specific retinal enzymes, but may also lead to a fuller understanding of visual pigment metabolism, and the factors which control or influence this process.